Activity monitoring

ABSTRACT

An activity monitor is provided that can be cheaper and require lower power than existing activity monitors. A single output channel from a plurality of motion sensors is provided and monitored intermittently.

The present invention relates to activity monitoring, and in particular,but not exclusively to, activity monitoring of a human being.

The physical activity of a human being is an important determinant ofits health. The amount of daily physical activity is considered to be acentral factor in the etiology, prevention and treatment of variousdiseases. Information about personal physical activity can assist theindividual in maintaining or improving his or her functional healthstatus and quality of life.

A known system for monitoring human activity is described in the article“A Triaxial Accelerometer and Portable Data Processing Unit for theAssessment of Daily Physical Activity”, by Bouten et al., IEEETransactions on Biomedical Engineering, Vol. 44, NO. 3, March 1997.

According to the known system a triaxial accelerometer composed of threeorthogonally mounted uniaxial piezoresistive accelerometers is used tomeasure accelerations covering the amplitude and frequency ranges ofhuman body acceleration. An individual wears the triaxial accelerometerover a certain period of time. A data processing unit is attached to thetriaxial accelerometer and programmed to determine the time integrals ofthe module of accelerometer output from the three orthogonal measurementdirections. These time integrals are summed up and the output is storedin a memory that can be read out by a computer. The output of thetriaxial accelerometer bears some relation to energy expenditure due tophysical activity and provides as such a measure for the latter.

The known system allows for measurement of human body acceleration inthree directions. Using state of the art techniques in the field ofintegrated circuit technology the accelerometer can be built small andlightweight allowing it to be worn for several days or even longerwithout imposing a burden to the individual wearing it.

The known systems continuously sample and monitor information from thethree accelerometers using three sample analog channels. Since themeasurement is carried out continuously, the power consumption of such adevice is undesirably high, and so it is desirable to reduce powerconsumption, which should enable cheaper and/or smaller batteries to beusable.

It is therefore desirable to provide an activity monitor that canovercome these disadvantages.

According to one aspect of the present invention, there is provided anactivity monitor comprising a measurement unit including a plurality ofmotion sensors, operable to produce respective sensor signals indicativeof motion experienced thereby and a processor for receiving the sensorsignals from the measurement unit and operable to process the signals inaccordance with a predetermined method, characterized in that themeasurement unit has a single output channel and is operable to outputthe sensor signals in turn on the output channel.

FIG. 1 shows a block diagram schematically showing the components of asystem embodying one aspect of the present invention;

FIG. 2 schematically shows the orthogonal outputs of threeaccelerometers;

FIG. 3 shows a flow diagram of the steps of a method embodying anotheraspect of the present invention; and

FIG. 4 illustrates monitoring of sensor signals in embodiments of thepresent invention.

FIG. 1 illustrates an activity monitor 1 embodying one aspect of thepresent invention. The activity monitor 1 comprises a measurement unit11, a processor 12, and a memory unit 13. The measurement unit 11 isoperable to produce data signals indicative of the motion of theactivity monitor 1, and to supply those data signals to the processor12. The processor 12 is operable to process the data signals output fromthe measurement unit, and is able to store the data signals, or Theresults of the processing in the memory unit 13. Data can be transferredbetween the processor and the memory unit 13. The processor 12 is alsoable to be connected to an external host system 2, which can be apersonal computer (PC) or other appropriate systems. The external hostsystem 2 can be used to perform additional processing of the data heldin the activity monitor 1.

In use, the activity monitor 1 is attached to the object to bemonitored. For purposes of illustration in the following it is assumedthat the object is a human individual, although it is clearly possibleto apply such an activity monitor for any object. The activity monitoris attached to the individual or object for a certain time period.

The measurement unit comprises three accelerometers which are arrangedin mutually orthogonal directions. The accelerometers output datasignals which are indicative of the respective accelerations experiencedby the accelerometers. The three accelerometers are arranged orthogonalto one another in a conventional manner.

On an individual, these directions are formed “antero-posterior”,“medico-lateral” and “vertical”, that are denoted as x, y and z,respectively, as shown in FIG. 2. The accelerometers comprise strips ofpiezo-electric material that is uni-axial and serial bimorph. The stripsare fixed at one end thereof.

The piezo-electric accelerometers act as damped mass-spring systems,wherein the piezo-electric strips act as spring and damper. Movements ofthe strips due to movement of the individual generate an electric chargeleading to a measurement of a data signal. In case of human movementsthe frequency of the data signals lies in the range of 0.1-20 Hz. Theamplitude of the data signals lies between −12 g and +12 g. Thesenumbers are discussed in more detail in the article mentioned earlier.Suitable piezo-electric materials to measure such data signals are knownto a person skilled in the art.

In accordance with the present invention, the measurement unit has asingle output channel, preferably a single analog output channel, whichis supplied to the processor 12. The measurement unit operates to outputone of the accelerometer signals at any one time via the output channel.The accelerometer signals are output in turn to the output channel viathe measurement unit.

In one preferred embodiment of the present invention, the processor isoperable to sample the output channel measurement unit in discontinuousfashion. In such a case, the processor samples the output channel fromthe measurement unit for a predetermined amount of time, and then stopssampling the measurement unit.

In addition to the processor unit operating discontinuously, or as analternative to that methodology, the measurement unit can operate theoutput channel discontinuously during the output of each accelerometersignal. FIG. 3 is a flow diagram illustrating the cycled outputs of themeasurement unit. As will be appreciated from FIG. 3, each of theoutputs a_(x), a_(y) and a_(z), are output in turn from the measurementunit. This is further illustrated in FIG. 4. For the sake of clarity, noparticular output signal is shown in FIG. 4, but the time periods duringwhich the respective accelerometer signals are output are shown.

It will be appreciated that reducing the number of channels requiredfrom the output of the measurement unit to the processor, can reduce thecost of the activity monitor overall. In addition, varying the samplingrate of the processor means that there are periods of time in which theprocessor is not active, and so battery power can be conserved duringthese times. Embodiments of the invention, therefore, can reduce thecost and/or battery power consumption of an activity monitor.

It will be readily appreciated that the accelerometers are merelypreferred motion sensors, and that any appropriate motion sensor couldbe used in an embodiment of the present invention and achieve theadvantages of the present invention.

It is emphasized that the term “comprises” or “comprising” is used inthis specification to specify the presence of stated features, integers,steps or components, but does not preclude the addition of one or morefurther features, integers, steps or components, or groups thereof.

1. An activity monitor comprising: a measurement unit including aplurality of motion sensors, operable to produce respective sensorsignals indicative of motion experienced thereby; and a processorconnected to the measurement unit by a single output channel, theprocessor being configured to receive on the single output channel ofthe measurement unit the sensor signals from the measurement unit andoperable to process the signals; wherein the measurement unit isconfigured to operate the single output channel discontinuously in timeduring output of each motion sensor output signal.
 2. The activitymonitor as claimed in claim 1, wherein the motion sensors areaccelerometers.
 3. The activity monitor as claimed in claim 1, whereinthe motion sensors are arranged to be mutually orthogonal.
 4. Theactivity monitor as claimed in claim 2 or 3, wherein the processor isoperable to sample the single output channel of the measurement unitdiscontinuously in time.
 5. A method of monitoring activity using aplurality of motion sensors which are operable to produce respectivesensor signals on a single channel for output to a processor, the sensorsignals being indicative of motion experienced thereby, the methodcomprising the acts of: operating the single channel discontinuously intime to produce the respective sensor signals discontinuously in time;monitoring the sensor signals provided on the single channeldiscontinuously in time; and processing the sensor signals.
 6. Themethod as claimed in claim 5, further comprising providing the sensorsignals on the single channel, wherein the monitoring act monitors inturn the sensor signals on the single channel.
 7. The method of claim 5,wherein the processing act samples the single output channel of ameasurement unit discontinuously in time, said single output channelincluding the sensor signals from the plurality of the motion sensors.8. The method of claim 5, wherein the processing act intermittentlysamples the single output channel of a measurement unit that outputs thesensor signals.
 9. An activity monitor comprising: a measurement unitincluding a plurality of motion sensors, operable to produce respectivesensor signals indicative of motion experienced thereby; and a processorconnected to the measurement unit by a single output channel, theprocessor being configured to receive the sensor signals from themeasurement unit on the single output channel and to process the sensorsignals in accordance with a predetermined method, wherein the processoris further configured to sample the single output channel of themeasurement unit discontinuously in time, and wherein the measurementunit is configured to operate the single output channel discontinuouslyin time during output of each motion sensor output signal.
 10. Theactivity monitor as claimed in claim 9, wherein the motion sensors areaccelerometers.
 11. The activity monitor as claimed in claim 9, whereinthe motion sensors are arranged to be mutually orthogonal.
 12. Theactivity monitor of claim 9, wherein the measurement unit is operable tooutput the sensor signals in turn on the single output channel.
 13. Amethod of monitoring activity using a plurality of motion sensors whichare operable to produce respective sensor signals on a single channelfor output to a processor, the sensor signals being indicative of motionexperienced thereby, the method comprising the acts of: operating thesingle channel discontinuously in time to produce the respective sensorsignals discontinuously in time; intermittently monitoring the sensorsignals; and processing the sensor signals.
 14. The method of claim 13,wherein the processing act intermittently samples the single channel ofa measurement unit, said single channel including the sensor signalsfrom the plurality of the motion sensors.
 15. An activity monitorcomprising: a measurement unit having a plurality of motion sensors thatproduce sensor signals indicative of motion; and a processor configuredto intermittently monitor the sensor signals; wherein the measurementunit is connected to the processor by a single output channel, thesensor signals being provided to the processor on the single outputchannel and the measurement unit being configured to operate the singleoutput channel discontinuously in time.